The present invention relates generally to limb occlusion devices. In particular, the present invention describes a limb occlusion device capable of performing more than one function, for example as a limb occlusion tourniquet, as a blood pressure monitor and as a device for automatic delivery of remote conditioning treatment.
Inflatable limb occlusion devices generally include a cuff sized to be placed about a limb such as an upper arm or a thigh of a subject and a controller operably connected to or incorporated with the cuff and configured for inflating and deflating the cuff to achieve a desired function. One example of such function may be to detect the subject's blood pressure by slowly inflating or deflating the cuff while recording oscillometric oscillations (also known as an oscillometric envelope) from which systolic, diastolic and mean arterial blood pressure of the subject may be determined—see FIG. 2. Another example of such desired function is to provide a more prolonged limb occlusion for the purpose of causing cessation of blood flow to the limb—for example during a knee surgery to provide a bloodless field or as an emergency tourniquet designed to stop blood loss through the bleeding extremity. Yet another example of such desired function may be to deliver a therapy called remote conditioning.
The term “remote conditioning” is used in this disclosure to describe a recently discovered therapy in which one or more limbs are subjected to a series of intermittent occlusions of blood flow followed by restorations of blood flow. The terms “limb occlusion” and “cessation” of blood flow are used in this disclosure to describe a reduction of 90% or more of the blood flow through the limb as compared with unrestricted blood flow. In a typical scenario, 5-min occlusion of blood flow to a certain limb such as an upper arm or a thigh is followed by 5-min release. This treatment cycle may be repeated 4 times making the entire procedure to last about 40 minutes. The duration or each occlusion and each release and the number of treatment cycles may vary: each occlusion and each release may last respectively from about 1 minute to about 20 min, and the number of treatment cycles may be from 2 to 20. The therapy of “remote conditioning” is sometimes referred to in the literature as “ischemic conditioning”, “remote ischemic conditioning”, “remote ischemic peri-conditioning”, “remote ischemic preconditioning”, “remote ischemic perconditioning”, or “remote ischemic postconditioning”, depending on whether this procedure is applied before or after either the initial occlusion event (such as for example an acute myocardial infarction or stroke) or a treatment of such event involving restoration of blood flow to the target organ. In any case, all of these modalities are generally referred to as remote conditioning in this description.
The therapy of remote conditioning has been demonstrated to be clinically beneficial in a variety of circumstances using a manually-operated blood pressure cuff. Many of such circumstances involve a clinical situation in which perfusion (normal blood flow to a target organ or tissue) is temporarily interrupted leading to ischemia (lack of oxygen delivery to the organ). This may occur either deliberately—during surgery for example—or as a result of a disease, for example a heart attack or stroke. Restoration of perfusion is known to trigger a so-called ischemia-reperfusion injury, which further exacerbates the original ischemic injury and increases infarct size—by as much as 50%. Prevention or at least attenuation of ischemia-reperfusion injury has valuable clinical benefits and remote conditioning is shown to be the most potent known method providing this benefit.
Remarkably, in over 100 published clinical trials of remote conditioning on over 10,000 patients worldwide, there are no reported side effects or complications associated with this non-invasive procedure making it especially attractive and safe to use.
Despite the fact that all three modalities described above (limb tourniquet, blood pressure monitor, and device for remote conditioning) may be accomplished by using an inflatable cuff, there are no known devices configured to accomplish more than one of these modalities. Well known are stand-alone blood pressure monitors, stand-alone limb occlusion tourniquets, and stand-alone remote conditioning devices. Yet, in many clinical circumstances, the subject may benefit if more than one modality is delivered on the same limb and by the same device. There is a need therefore for a multi-mode inflatable limb occlusion device that may provide any two or all three operating modes described above.